- Heartburn Slideshow: Foods to Eat, Foods to Avoid
- 10 Facts About the Amazing Brain
- Weight Gain Shockers Slideshow Pictures
What facts should I know about drug interactions?
Whenever two or more drugs are being taken, there is a chance that there will be an interaction among the drugs. The interaction may increase or decrease the effectiveness of the drugs or their side effects. The likelihood of drug interactions increases as the number of drugs being taken increases. Therefore, people who take many drugs are at the greatest risk for interactions. Drug interactions contribute to the cost of healthcare because of the costs of medical care that are required to treat problems caused by changes in effectiveness or side effects. Interactions also can lead to psychological suffering. This review discusses the issue of drug interactions and several ways to avoid them.
What are drug interactions?
A drug interaction can be defined as an interaction between a drug and another substance that prevents the drug from performing as expected. This definition applies to interactions of drugs with other drugs (drug-drug interactions), as well as drugs with food (drug-food interactions) and other substances, such as supplements. Drugs also may interact with laboratory tests, changing the proper results of the laboratory test.
How do drug interactions occur?
There are several mechanisms by which drugs interact with other drugs, food, and other substances. An interaction can result when there is an increase or decrease in:
- the absorption of a drug into the body;
- distribution of the drug within the body;
- alterations made to the drug by the body (metabolism); and
- elimination of the drug from the body.
Most of the important drug interactions result from a change in the absorption, metabolism, or elimination of a drug. Drug interactions also may occur when two drugs that have similar (additive) effects or opposite (canceling) effects on the body are administered together. For example, there may be major sedation when two drugs that can cause sedation are taken simultaneously, such as narcotics with antihistamines.
Another source of drug interactions occurs when one drug alters the concentration of a substance that is normally present in the body. The alteration of this substance reduces or enhances the effect of another drug that is being taken. The drug interaction between warfarin (Coumadin) and vitamin K-containing products is a good example of this type of interaction. Warfarin acts by reducing the concentration of the active form of vitamin K in the body. Therefore, when vitamin K is taken, it reduces the effectiveness of warfarin.
Change in absorption
Most drugs are absorbed into the blood and then travel to their site of action. Most drug interactions that are due to altered absorption occur in the intestine. There are various ways that the absorption of drugs can be reduced. These mechanisms include:
- an alteration in blood flow to the intestine;
- change in drug metabolism (breakdown) by the intestine;
- increased or decreased intestinal motility (movement);
- alterations in stomach acidity, and
- a change in the bacteria that normally reside in the intestine.
Drug absorption also can be affected if the drug's ability to dissolve (solubility) is changed by another drug or if a substance (for example, food) binds to the drug and prevents its absorption.
Change in drug metabolism and elimination
Most drugs are eliminated through the kidney in either an unchanged form or metabolized by the liver. Therefore, the kidney and the liver are very important sites of potential drug interactions. Some drugs are able to reduce or increase the metabolism of other drugs by the liver or their elimination by the kidney.
Metabolism of drugs is the process through which the body converts (alters or modifies) drugs into forms that are more or less active (for example, by converting drugs that are given in inactive forms into their active forms that actually produce the desired effect) or that are easier for the body to eliminate through the kidneys. Most drug metabolism takes place in the liver, but other organs also may play a role (for example, the kidneys, intestine, etc.). The cytochrome P450 enzymes are a group of enzymes in the liver that are responsible for the metabolism of most drugs. They are, therefore, often involved in drug interactions. Drugs and certain types of food may increase or decrease the activity of these enzymes and therefore affect the concentration of drugs that are metabolized by these enzymes. An increase in the activity of these enzymes leads to a decrease in the concentration and effect of an administered drug. Conversely, a decrease in enzyme activity leads to an increase in drug concentration and effect.
How often do drug interactions occur?
The prescribing information for most drugs contains a list of potential drug interactions. Many of the listed interactions may be rare, minor, or only occur under specific conditions and may not be important. Drug interactions that cause important changes in the action of a drug are of greatest concern.
Drug interactions are complex and often unpredictable. A known interaction may not occur in every individual. This can be explained because there are several factors that affect the likelihood that a known interaction will occur. These factors include differences among individuals in their:
- lifestyle (diet, exercise),
- underlying diseases,
- drug doses,
- the duration of combined therapy, and
- the relative time of administration of the two substances. (Sometimes, interactions can be avoided if two drugs are taken at different times.)
Nevertheless, important drug interactions occur frequently and they add millions of dollars to the cost of health care. Moreover, many drugs have been withdrawn from the market because of their potential to interact with other drugs and cause serious health care problems.
What are the consequences of drug interactions?
Drug interactions may lead to an increase or decrease in the beneficial or the adverse effects of the given drugs. When a drug interaction increases the benefit of the administered drugs without increasing side effects, both drugs may be combined to increase the control of the condition that is being treated. For example, drugs that reduce blood pressure by different mechanisms may be combined because the blood pressure lowering effect achieved by both drugs may be better than with either drug alone.
The absorption of some drugs is increased by food. Therefore, these drugs are taken with food in order to increase their concentration in the body and, ultimately, their effect. Conversely, when a drug's absorption is reduced by food, the drug is taken on an empty stomach.
Drug interactions that are of greatest concern are those that reduce the desired effects or increase the adverse effects of the drugs. Drugs that reduce the absorption or increase the metabolism or elimination of other drugs tend to reduce the effects of the other drugs. This may lead to failure of therapy or warrant an increase in the dose of the affected drug. Conversely, drugs that increase absorption or reduce the elimination or metabolism of other drugs - increase the concentration of the other drugs in the body - and lead to increased amounts of drug in the body and more side effects. Sometimes, drugs interact because they produce similar side effects. Thus, when two drugs that produce similar side effects are combined, the frequency and severity of the side effect are increased.
Subscribe to MedicineNet's General Health Newsletter
How can drug interactions be avoided?
- Give healthcare professionals a complete list of all of the drugs that you are using or have used within the last few weeks. This should include over-the-counter medications, vitamins, food supplements, and herbal remedies.
- Inform healthcare professionals when medications are added or discontinued.
- Inform healthcare professionals about changes in lifestyle (for example, exercise, diet, alcohol intake.
- Ask your healthcare professionals about the most serious or frequent drug interactions with the medications that you are taking.
- Since the frequency of drug interactions increases with the number of medications, work with your healthcare professionals to eliminate unnecessary medications. Always discuss potential drug interactions with our pharmacist.
This brief overview of drug interactions does not cover every possible scenario. Individuals should not be afraid to use their drugs because of the potential for drug interactions. Rather, they should use the information that is available to them to minimize the risk of such interactions and to improve the success of their therapy.
Drug interactions occur frequently. Get facts about the types of drug interactions, what substances or other things that may interact with drugs such as OTC drug and prescription drugs, vitamins, food(s) (grapefruit), and laboratory tests. Find out how to protect yourself from potential drug interactions.
Multimedia: Slideshows, Images & Quizzes
Dementia, Alzheimer's Disease, and Aging Brains
What is dementia? Learn about dementia disorders such as Lewy Body Dementia, Alzheimer's disease (AD), Vascular (multi-infarct)...
Picture of Phototoxic Drug-induced Photosensitivity
Topical Phototoxic Dermatits is inadvertent contact with or therapeutic application of a photosensitizer, followed by UVA...
Picture of Phototoxic Drug Reaction
In phototoxic reactions, the drug may become activated by exposure to sunlight and cause damage to the skin. See a picture of...
Cholesterol Drugs: What to Expect With Heart Medication
When diet and exercise aren't enough, should you turn to drugs? Learn cholesterol basics, drug classes, and available drugs along...
Asthma Symptoms, Causes, and Medications
What is asthma? Learn about asthma, a chronic inflammation disorder of the bronchiole tubes (airways). Discover information about...
Addicted to Pills: The Health Risks of Drug Abuse
What is drug abuse? Learn about prescription drug abuse and over-the-counter (OTC) drugs, including depressants, pain relievers,...
Related Disease Conditions
Headaches can be divided into two categories: primary headaches and secondary headaches. Migraine headaches, tension headaches,...
Migraine headache is a type of headache associated with a sensitivity to light, smells, or sounds, eye pain, severe pounding on...
Heart disease (coronary artery disease) occurs when plaque builds up in the coronary arteries, the vessels that supply blood to...
Malaria is a disease that is spread by the bite of an infected Anopheles mosquito. Malaria symptoms include fever, chills,...
Fibromyalgia is a chronic pain condition characterized by symptoms such as fatigue, sleep disturbances, and tender points. Stress...
Dementia is defined as a significant loss of intellectual abilities such as memory capacity, severe enough to interfere with...
Asthma: Over the Counter Treatment
Patients who have infrequent, mild bouts of asthma attacks may use over-the-counter (OTC) medications to treat their asthma...
Sun-Sensitive Drugs (Photosensitivity to Drugs)
Sun sensitivity (photosensitivity) is an inflammation of the skin induced by the combination of medications or substances and...
Pain management and treatment can be simple or complex, according to its cause. There are two basic types of pain, nociceptive...
Asthma is a condition in which hyperreactive airways constrict and result in symptoms like wheezing, coughing, and shortness of...
Atrial Fibrillation (AFib) Symptoms, ECG, and Treatment Medications
Atrial fibrillation (AF or AFib) is an abnormality in the heart rhythm which involves irregular and often rapid beating of the...
Insomnia (Symptoms, Causes, Remedies, and Cures)
Insomnia is the perception or complaint of inadequate or poor-quality sleep because of difficulty falling asleep; waking up...
There are two types of asthma medications: long-term control with anti-inflammatory drugs and quick relief from bronchodilators....
Heart Attack Treatment
A heart attack involves damage or death of part of the heart muscle due to a blood clot. The aim of heart attack treatment is to...
Insomnia Treatment (Sleep Aids and Stimulants)
Insomnia is difficulty in falling or staying asleep, the absence of restful sleep, or poor quality of sleep. Insomnia is a...
Drug Allergy (Medication Allergy)
Drug or medication allergies are caused when the immune system mistakenly creates an immune response to a medication. Symptoms of...
Pregnancy and Drugs (Prescription and OTC)
Taking prescription medications or over-the-counter drugs or supplements should be discussed with your doctor. There are some...
Treatment & Diagnosis
Medications & Supplements
- Nonsteroidal Antiinflammatory Drugs (NSAIDs)
- prednisone (Prednisone Intensol, Rayos) Corticosteroid
- metronidazole (Flagyl, Flagyl ER) Antibiotic
- Proton Pump Inhibitors (PPIs) Drug Class
- Sertraline (Zoloft)
- ACE Inhibitors (Side Effects, List of Names, Uses, and Dosage)
- Beta Blockers (Drug Class, List of Brand and Generic Names)
- Cipro, Cipro XR (ciprofloxacin) Antibiotic Side Effects
- Aldactone (spironolactone)
- cephalexin (Keflex)
- Tramadol: for Pain (Ultram, Ultram ER, Conzip)
- hydroxyzine (Vistaril)
- alprazolam (Xanax, Xanax XR, Niravam) Anti-Anxiety Drug
- codeine (for Pain)
- Angiotensin II Receptor Blockers (ARBs)
- clonazepam (Klonopin)
- pantoprazole (Protonix)
- naproxen (Aleve, Anaprox, Naprelan, Naprosyn)
- nitrofurantoin (Macrodantin, Furadantin, Macrobid)
- gabapentin (Neurontin)
- furosemide (Lasix)
- metoprolol (Lopressor, Toprol XL)
- acetaminophen (Tylenol, Tylenol Arthritis Pain, Tylenol Ext, Little Fevers Children's Fever/Pain)
- amitriptyline (Elavil, Endep)
- Levaquin (levofloxacin) Antibiotic
- cefdinir (Omnicef has been discontinued)
- amoxicillin (Amoxil, Moxatag, Larotid)
- meloxicam (Mobic) Side Effects
- Oxycodone for Pain (OxyContin, Roxicodone, Oxecta, Oxaydo, Xtampza ER, Roxybond)
- digoxin (Lanoxin, Lanoxin Pediatric)
- diphenhydramine, Benadryl
- modafinil (Provigil)
- losartan (Cozaar)
- Anxiolytics (for Anxiety) Drug Class Side Effects
- celecoxib (Celebrex)
- trazodone (Desyrel - discontinued brand)
- Cox-2 Inhibitors
- temazepam (Restoril)
- benzonatate (Tessalon Perles)
- Lipitor (atorvastatin)
- mupirocin (Bactroban, Centany)
- lorazepam (Ativan)
- ibuprofen (Advil, Children's Advil/Motrin, Medipren, Motrin, Nuprin, PediaCare Fever, and others)
- ipratropium bromide inhaler (Atrovent)
- citalopram, Celexa
- bupropion (Wellbutrin, Wellbutrin SR, Wellbutrin XL, Zyban, Aplenzin, Fortivo XL, Zyban)
- metformin (Glucophage, Glucophage XR, Glumetza, Fortamet, Riomet)
- Diflucan (fluconazole)
- diazepam (Valium, Diastat, Acudial, Diastat Pediatric, Diazepam Intensol)
- loratadine, Claritin, Claritin RediTabs, Alavert, Claritin Hives Relief, Children's Claritin
- Aspirin vs. Plavix (clopidogrel)
- lisinopril (Zestril, Prinivil, Qbrelis) ACE Inhibitor
- haloperidol (Haldol)
- levothyroxine sodium (Synthroid, Levoxyl)
- Calcium Channel Blockers (CCBs)
- Carafate (sucralfate)
- Valtrex (valacyclovir)
- Percocet (oxycodone and acetaminophen, Roxicet, Tylox, Oxycet)
- albuterol (Ventolin, Proventil)
- azithromycin (Zithromax, Zithromax Z-Pak, Zithromax Tri-Pak, Zmax)
- baclofen (Gablofen, Lioresal)
- carvedilol (Coreg)
- montelukast, Singulair
- erythromycin (Ery-Tab, PCE)
- Viagra (sildenafil)
- venlafaxine, Effexor XR (Effexor has been discontinued in the US)
- omeprazole (Prilosec, Zegerid)
- dicyclomine, Bentyl
- hydrocodone/acetaminophen (Vicodin, Norco)
- tretinoin (Retin-A, Retin-A Micro, Atralin, Renova, Avita)
- mirtazapine (Remeron, Soltab)
- simethicone, Phazyme, Mi-Acid, Gas Relief, Mytab Gas, Gas-X, Gas-X Extra Strength
- buspirone (Buspar)
- amlodipine (Norvasc)
- diphenoxylate and atropine (Lomotil)
- clonidine (Catapres, Catapres-TTS)
- lansoprazole (Heartburn Relief 24 Hour, Heartburn Treatment 24 Hour, Prevacid 24)
- captopril (Capoten)
- cefixime (Suprax)
- cyclobenzaprine (Flexeril, Amrix, Fexmid)
- Flomax (tamsulosin)
- glucose (Insta-Glucose, Dex4, Enfamil Glucose, Glutol, Glutose and many others)
- sumatriptan, Imitrex, Alsuma, Imitrex STATdose System, Sumavel DosePro
- amiodarone, Cordarone, Nextrone, Pacerone
- rituximab (Rituxan)
- clopidogrel (Plavix)
- fluvoxamine (Luvox)
- nifedipine (Procardia, Adalat, Afeditab)
- triamterene and hydrochlorothiazide
- colestipol (Colestid)
- Tramadol (Ultram) Side Effects
- hydrochlorothiazide (Microzide, Hydrodiuril)
- isosorbide mononitrate, Imdur, Ismo, Monoket
- mesalamine (Pentasa, Rowasa, SfRowasa, Lialda, Canasa, Apriso, Delzicol)
- betamethasone dipropionate, Diprolene; Diprolene AF
- Zocor (simvastatin)
- Actos (pioglitazone)
- alteplase (TPA, Activase, Cathflo Activase)
- diltiazem (Cardizem, Cardizem CD, Cardizem LA, Tiazac, Cartia XT, Diltzac, Dilt-CD, and several oth)
- misoprostol, Cytotec
- phentermine (Adipex-P)
- warfarin (Coumadin, Jantoven)
- calcium carbonate (Caltrate 600, Os-Cal 500, Tums)
- risedronate (Actonel, Atelvia)
- loperamide (Imodium)
- metoclopramide, Reglan, Metozolv ODT, (Reglan ODT, Octamide, and Maxolon
- fentanyl patch (Duragesic)
- fluticasone (Flonase, Flonase Allergy Relief)
- Amaryl (glimepiride)
- promethazine and codeine, Phenergan with Codeine
- chlorthalidone (Thalitone)
- budesonide (oral inhalation, Pulmicort, Pulmicort Flexhaler)
- felodipine (Plendil)
- topiramate, Topamax, Qudexy XR, Topamax Sprinkle, Topiragen, Trokendi XR
- quetiapine (Seroquel, Seroquel XR)
- benazepril (Lotensin HTC)
- bisoprolol, Zebeta
- fexofenadine (Allegra, Mucinex Allergy)
- prednisolone (Orapred, Pediapred)
- tamoxifen (Soltamox, Nolvadex)
- Lotrisone (clotrimazole and betamethasone topical cream and lotion)
- orlistat (Xenical, Alli)
- Strattera (atomoxetine)
- glipizide, Glipizide XL, Glucotrol, Glucotrol XL
- carisoprodol (Soma)
- sulfasalazine (Azulfidine)
- isosorbide dinitrate (Isordil Titradose)
- glucagon recombinant (GlucaGen)
- carbamazepine, Tegretol, Tegretol XR , Equetro, Carbatrol, Epitol, Teril
- lithium, Lithobid
- zolpidem (Ambien)
- nortriptyline, Pamelor, Aventyl - has been discontinued in the U.S.
- triazolam (Halcion)
- timolol ophthalmic solution (Timoptic)
- cyclophosphamide (Cytoxan)
- isotretinoin (Accutane, Claravis, Amnesteem, Absorica, Zenatane)
- pentoxifylline (Trental, Pentoxil)
- clozapine (Clozaril, Fazacio ODT, Versacloz)
- flurbiprofen (Ansaid)
- nadolol (Corgard)
- tacrolimus (Prograf, Astagraf XL, Envarsus XR)
- Precose (acarbose)
- estradiol, Alora, Climara, Delestrogen, Depo-Estradiol, Divigel, Elestrin, Estrace, and Others
- hydrocortisone valerate
- oseltamivir (Tamiflu)
- repaglinide (Prandin)
- loratadine and pseudoephedrine (Alavert Allergy & Sinus, Claritin-D, Claritin-D 24 hour)
- penicillin V, (Veetids and Pen-Vee-K have been discontinued)
- Lotrel (amlodipine and benazepril)
- terconazole, Terazol, Zazole
- gemfibrozil (Lopid)
- budesonide (Entocort EC, Uceris)
- propafenone (Rythmol)
- desipramine, Norpramin
- anakinra, Kineret
- chlorpheniramine and hydrocodone, Tussionex, TussiCaps, Tussionex Pennkinetic, Vituz
- Primsol (trimethoprim)
- fenoprofen, Nalfon
- cefprozil (Cefzil)
- beclomethasone dipropionate inhaler (Qvar)
- minoxidil (Rogaine)
- imipramine (Tofranil)
- OTC Pain Relievers and Fever Reducers
- nefazodone, Serzone
- medroxyprogesterone, Provera, Depo-Provera, Depo-Sub Q Provera 104
- chlordiazepoxide hydrochloride and clidinium bromide (Librax)
- oxaprozin, Daypro
- Herceptin (trastuzumab)
- Sectral (acebutolol)
- hylan G-F 20 (Synvisc, Synvisc One)
- Advair Diskus, Advair HFA (fluticasone and salmeterol oral inhaler)
- Evista (raloxifene)
- budesonide nasal inhaler (Rhinocort Allergy, Rhinocort Aqua)
- atenolol and chlorthalidone, Tenoretic
- ribavirin, Rebetol, Copegus, Ribasphere, RibaPak, Moderiba
- fluorouracil (Carac, Efudex, Fluoroplex, Tolak)
- quinidine (Discontinued Brands: Cardioquine, Cin-Quin, Duraquin, Quinidex, Quinora, Quinact)
- zanamivir, Relenza
- salsalate, Amigesic, Salflex, Argesic-SA, Marthritic, Salsitab, Artha-G
- pramoxine (Itch-X, PrameGel, Orax, Sarna Sensitive, and Others)
- zafirlukast (Accolate)
- timolol (Blocadren and Timolide 10-25 have been discontinued)
- chlorpropamide, Diabinese
- Didronel (etidronate)
- estropipate, Ogen
- procainamide, Pronestyl; Procan-SR; Procanbid (These brands no longer are available in the U.S.)
- Combivir (lamivudine and zidovudine)
- lamivudine (3tc) (Epivir; Epivir HBV)
- choline magnesium salicylate, Trilisate
- miglitol, Glyset
- meclofenamate; Meclomen
- rimantadine, Flumadine
- bitolterol mesylate, Tornalate
- Retrovir (zidovudine, ZDV, formerly called AZT)
- bepridil (Vascor, Bepadin - Discontinued)
Prevention & Wellness
- Drug Companies Raise Prices on More Than 1,000 Medicines
- Seniors on Multiple Meds a Driving Hazard
- Drug Studies in Children Often Go Unfinished: Study
- Trump to Sign Bills Lifting Drug Price 'Gag Orders' on Pharmacists
- FDA Issues Warning on Pet Reactions to Common Flea Medicine
- Timing May Be Critical When Taking Meds
- As U.S. Kids Take More Meds, Dangerous Drug Mixes Could Rise
- Health Tip: Grapefruit May Interact With Medication
- Dilemma for Cancer Patients as Life-Saving Meds Are Tied to Vision Loss
- Could Nonprofit Drug Companies Cut Sky-High Prices?
- Antibiotics Tied to Higher Kidney Stone Risk
- Generic Drugs Don't Always Push Prices Down
- Health Tip: Prevent an Accidental Drug Overdose
- Daily Aspirin Can Bring Heart Benefits, But Risks Too
- What You Don't Know About Drug Interactions Could Hurt You
- Opioid Abuse Down in Younger Americans, But Up Among Older Adults
- Preparing for Anesthesia: 5 Tips You Should Know
- Marijuana Derivative May Curb Tough-to-Treat Epilepsy
- These Medicines Often Send Americans to ERs
- Health Tip: Be Aware of Drug and Food Interactions
- Statins Often Interact With Other Heart Drugs
- How Older People Can Head Off Dangerous Drug Interactions
- Falls a Growing and Deadly Threat for Older Americans
- Over 100 Drugs Pose Risk to Heart Failure Patients
- Health Tip: Lower Your Risk of Drug Interactions
- 1 in 6 Seniors Takes Dangerous Combos of Meds, Supplements: Study
- Can You Trust Your Dietary Supplement?
- Too Many Seniors With Diabetes Are Overtreated, Study Suggests
- Doctors' Prescribing Practices Key to Curbing Painkiller Abuse: CDC
- Taking St. John's Wort for Depression Carries Risks: Study
- Antibiotic May Lower Effect of Some Blood Thinners
- FDA Warns of Cardiac Effect When Heart Drug Mixed With Hepatitis C Meds
- Certain Heart Drug, Antibiotic Combo Might Be Fatal for Seniors
- Many Consumers Misled About Bogus Weight-Loss Supplements, Survey Says
- Drug Interactions Common Among Hospitalized Kids, Study Says
- U.S. Prices Soaring for Some Generic Drugs, Experts Say
- Why Aren't There Sex Drugs for Women?
- Hepatitis C Combo Pill May Cure Those Who Can Afford It
- HIV Patients Less Likely to Get Cancer Treatment: Study
- Medication Safety Essential For Seniors
- New Drug May Help Lower 'Bad' Cholesterol Beyond Statins
- Prescription Drug Use Continues to Climb in U.S.
- Health Tip: When Food and Drugs Interact
- New Blood Pressure Guidelines Raise the Bar for Taking Medications
- Smartphones May Help Nursing Home Docs Spot Drug Mishaps
- Ice Pops Interfered With Hospital Patient's Lab Tests: Report
- Statins Plus Certain Antibiotics May Set Off Toxic Reaction: Study
- Report Details Steps to Boost Patient Safety
- Inconsistency Seen in Safety Labeling for Generic Drugs
- Heart Drug Digoxin Tied to Higher Death Risk for Some Patients
- More New Drugs a Bad Fit With Grapefruit, Study Finds
- FDA Mulls Expanding Patients' Access to Certain Drugs
- Herbal Medicines for Arthritis Not Backed by Evidence
- New Guidelines Issued for Combining HIV, Seizure Meds
- New Drug Helps Patients With Atrial Fibrillation
Health Solutions From Our Sponsors
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
FDA Prescribing Information.